Aspects of the present invention generally relate to the detection of undesired contaminants in fluid flows within structures such as pipelines and vessels, using electromagnetic waves. More specifically, aspects of the present invention relate to the real-time detection and monitoring of black powder contaminants within gas flows in natural gas pipelines. Conventional systems for detecting undesired contaminants generally function by transmitting and receiving an electromagnetic signal through a multiphase flow, and inferring the dielectric properties of the flow based on the amplitude and phase change of the received signal. Such detectors also function by deducing flow properties based on the shift of the resonance frequency as well as the quality factor in the transmitted signal.
Pipelines and vessels are typically made out of either metallic materials (e.g., steel) or non-metallic materials (e.g., plastics and composites). Such structures are used extensively for fluid transmission in many industries including the oil and gas industry. When used for natural gas transmission, steel pipelines are susceptible to undesired solid contaminants in the form of black powder carried within the gas flow. Black powder is a general term used to describe dry or wet fine powder material, e.g., solid particles, consisting of various corrosion products such as iron oxides, iron sulfides, and other contaminants such as dirt and sand. Black powder is a recognized threat to the integrity and operation of transmission pipelines in many different regions around the world.
Although the formation mechanism of black powder can vary, those skilled in the art believe that the initiation of black powder can be attributed at least in part to the hydrotesting phase during the pipeline commissioning stage. Regardless of how it originates, black powder adversely impacts the integrity of gas pipelines and the controls and instrumentation associated with the pipelines, which may lead to partial or even complete shutdown and lost production. For example, black powder accumulation causes valve damage, compressor failure, and instrumentation clogging leading to expensive repairs. In many instances, black powder contaminants propagate further to downstream processes and utility companies. In addition to potential physical asset damage, the propagation of the contaminants raises critical quality-of-service complaints and flow assurance concerns which may reflect negatively upon the image of the supplier.
Black powder is currently only discoverable through examining the consequences of its presence in a given pipeline section, such as by end-user complaints, or by discovering the indications of black powder residuals by inspecting components such as a failed compressor, a clogged flow meter, or a due-for-replacement line filter. After detecting black powder in a particular pipeline, it is typically managed, i.e., removed from the victim line, through routine pipeline maintenance procedures using various well-established methods such as filtration, gel-based or surface active agents-based cleaning and aggressive pigging. This, however, does not solve the problem completely because the discovered black powder in the cleaned line might have originated from a different pipeline in the network and transported with the flow to the victim line. Due to the lack of effective black powder detection methods, the source of the black powder is rarely discovered and hence not treated. Consequently, the problem soon arises again and repairs on the victim lines must be repeated.
The black powder flow in a gas pipeline is a two-phase (solid-gas) dielectric mixture. The presence of black-powder in the pipeline changes the effective medium in the pipe cross section. There is no doubt that the black powder particles have physical and chemical properties that are distinct from the host gas carrying the black powder. Such chemical or physical contrasts can be the basis for many detection methods. In principle, the contrast in the magnetic, electrical, electromagnetic, optical, thermal, and mechanical properties between the black powder and its host gas can be exploited to develop viable detection techniques. For instance, differential weight measurements have been used to measure black powder deposits in gas pipelines. Unfortunately, this method is not applicable for detecting the black powder in motion with the gas flow as desired in many applications. Ultraviolet and visual spectrometers have also been used to detect liquids in gas flows.
Previously, microwave measurement techniques for multiphase mixture characterization and liquid flow metering have been employed in many multiphase metering technologies and liquid flow sensors, alone as well as combined with other methods such as gamma rays. Although microwave techniques are particularly promising for multi-phase component fraction measurements, current solutions are lacking.
In general, determining multiphase component fractions using microwave methods is founded on the electromagnetic interaction between the electromagnetic waves and the dielectric medium in the pipe. Conventional methods of deducing the dielectric properties of the multiphase mixture at microwave frequencies are generally based on two approaches. In the first approach, the dielectric properties, i.e. permittivity, of the multiphase flow are inferred from amplitude and phase change of a microwave signal passing through the flow or reflected from the flow. In the second approach, these properties are deduced from the shift of the resonance frequency and change in the quality factor of a microwave resonant cavity containing the multiphase flow.
These conventional techniques have several shortcomings. For example, they cannot be applied to detect black powder within pressurized natural gas flows. In particular, the techniques do not address the significant problem of coping with high pressure applications. Furthermore, they either use the pipeline as a waveguide cavity resonator, or they are based on resonant inserts placed in the flow, which tend to perturb the process flow and decrease measurement accuracy. Also, most of these methods are limited to metallic pipelines.
Additionally, many techniques predict the flow properties from either detecting a shift in the resonance frequency, Doppler frequency shift, and/or detecting the attenuation of the microwave signal between two measurement points along flow direction. But these techniques have not been demonstrated as capable of detecting very small black powder flow rates, such as rates at less than 1 g/s typically encountered in practice